This invention relates to a radio signal receiving method of a radio communication system using pulse signals, and a radio signal receiver.
In a UWB (Ultra Wideband) system, for example, communication is conducted generally by using pulse signals. A receiver restores transmitted information by conducting correlation detection of a reception signal and a template pulse by using the template pulse corresponding to a pulse waveform.
Win, M. Z.; Scholtz, R. A, “Impulse radio: how it works”, IEEE Communications Letters, February, 1998, Volume: 2, Issue: 2 describes a UWB communication system that modulates Gaussian mono pulses by a PPM (Pulse Position Modulation) system.
In the PPM system, transmission is made while the position of the pulse waveform on a time axis is changed by a predetermined value (δ) in accordance with information to be transmitted. The receiver performs correlation detection by using the reception waveform and the template pulse and takes out the information. FIG. 14 shows typical demodulation flow of the PPM system. The template pulse (132) is created by synthesizing a reception waveform (130) when the information is 0 and a waveform obtained by inverting the phase of a reception waveform (131) when the information is 1. This template pulse will be hereinafter referred to as a “reference template”. When a correlation value of this reference template and the reception signal is integrated, an output becomes positive (133) when the transmitted signal is 0 and negative (134) when the signal is 1.
The template waveform used for reception in the prior art system remains the same in all the propagation environments. Consequently, the correlation detection output decreases at places at which a reception waveform is distorted by influences of multi-paths and reception characteristics are deteriorated.